Faujasite is a synthetic sodium aluminosilicate having a three dimensional network of channels and hollow space. Because of its chemical composition and structure as well as temperature resistance and modifiability faujasite has extraordinary catalytic properties, which make possible its use for example in cracking catalysts.
In the employment in cracking catalysts X-ray graphic phase purity, degree of crystallinity, SiO.sub.2 /Al.sub.2 O.sub.3 ratio and absorption properties play a central roll. (German AS 1203239, German patent 1098929, German patent 1038016).
It is known to produce seed mixtures for the synthesis of faujasite from water, alkali metal hydroxide, silica and aluminum oxide by mixing together sodium silicate and sodium aluminate (German patent 1930705, U.S. Pat. No. 4,228,137, U.S. Pat. No. 3,433,589).
The production of this seed mixture presupposes an exact dosage of the components. According to Example 1 of German patent 1930705 the ratio of the components is Na.sub.2 O:Al.sub.2 O.sub.3 :SiO.sub.2 :H.sub.2 O=15:1:15:165. As a disadvantage slight deviations therefrom already lead to lack of crystallization. Besides this pumpable mixture occasionally gels to a compact mass which can only be converted again to the pumpable condition with loss of the seeding properties.
There are known from U.S. Pat. No. 4,228,137 seed mixtures of the composition Na.sub.2 O:Al.sub.2 O.sub.3:SiO.sub.2 :H.sub.2 O=11:1:11.3:240) which are produced from calcined clays. A disadvantage thereby is that only special types of clays possess seed properties after the calcination and, as natural products, are always subject to deviation in their chemical composition. Impurities with foreign ions can likewise act disadvantageously on the seed properties.
From German OS 2145800 there is known a process for the production of nuclei centers in which sodium aluminate liquor is present and sodium silicate solution is added. This mixture is aged for 24 hours at room temperature.
The known process has the disadvantage that because of the different contents of the aluminate liquor an increased analytical expense and dosing problems arise.
Dosing problems above all arise from the fact that for the establishment of a specific SiO.sub.2 /Al.sub.2 O.sub.3 ratio with narrow tolerance limits there must be added a small amount of Al.sub.2 O.sub.3 in the aluminate liquor to a large amount of sodium silicate in the solution.
From German patent 3311339 there is known a process for the production of a seed mixture for the faujasite synthesis in which amorphous, synthetic sodium aluminum silicate is reacted with a Na.sub.2 O supplying compound.